How to make a Rust vanish plugin (admin invisibility)

using System.Linq;
using System;
using System.Collections.Generic;
using Newtonsoft.Json;
using Oxide.Core;
using Oxide.Game.Rust.Cui;
using UnityEngine;

namespace Oxide.Plugins
{
    [Info("Vanish", "RustPluginGenerator", "1.0.0")]
    [Description("Lets admins hide from players with a damage-proof vanish toggle and a small CUI indicator.")]
    public class Vanish : RustPlugin
    {
        private const string PermUse = "vanish.use";
        private const string IndicatorName = "vanish.indicator";

        private PluginConfig config;
        private readonly HashSet<ulong> vanished = new HashSet<ulong>();

        private class PluginConfig
        {
            [JsonProperty("Block Damage While Vanished")]
            public bool BlockDamage { get; set; } = true;

            [JsonProperty("Show Indicator")]
            public bool ShowIndicator { get; set; } = true;
        }

        protected override void LoadDefaultConfig() => config = new PluginConfig();

        protected override void LoadConfig()
        {
            base.LoadConfig();
            try
            {
                config = Config.ReadObject<PluginConfig>();
                if (config == null) throw new Exception();
            }
            catch
            {
                PrintWarning("Configuration file is invalid, using defaults");
                LoadDefaultConfig();
            }
            SaveConfig();
        }

        protected override void SaveConfig() => Config.WriteObject(config);

        protected override void LoadDefaultMessages()
        {
            lang.RegisterMessages(new Dictionary<string, string>
            {
                ["Enabled"] = "Vanish enabled. You are invisible and cannot take damage.",
                ["Disabled"] = "Vanish disabled. You are visible again.",
                ["NoPermission"] = "You do not have permission to use /vanish.",
                ["Indicator"] = "VANISHED"
            }, this);
        }

        private string Msg(string key, string userId = null, params object[] args) => string.Format(lang.GetMessage(key, this, userId), args);

        private void Init()
        {
            permission.RegisterPermission(PermUse, this);
        }

        [ChatCommand("vanish")]
        private void CmdVanish(BasePlayer player, string command, string[] args)
        {
            if (player == null) return;
            if (!permission.UserHasPermission(player.UserIDString, PermUse))
            {
                player.ChatMessage(Msg("NoPermission", player.UserIDString));
                return;
            }

            if (vanished.Contains(player.userID.Get()))
                Disappear(player);
            else
                VanishPlayer(player);
        }

        private void VanishPlayer(BasePlayer player)
        {
            vanished.Add(player.userID.Get());
            player.SetPlayerFlag(BasePlayer.PlayerFlags.Spectating, true);
            player.SendNetworkUpdate();
            player.ChatMessage(Msg("Enabled", player.UserIDString));

            if (config.ShowIndicator)
                ShowIndicator(player);
        }

        private void Disappear(BasePlayer player)
        {
            vanished.Remove(player.userID.Get());
            player.SetPlayerFlag(BasePlayer.PlayerFlags.Spectating, false);
            player.SendNetworkUpdate();
            player.ChatMessage(Msg("Disabled", player.UserIDString));
            CuiHelper.DestroyUi(player, IndicatorName);
        }

        private void ShowIndicator(BasePlayer player)
        {
            CuiHelper.DestroyUi(player, IndicatorName);

            var container = new CuiElementContainer();
            var panel = container.Add(new CuiPanel
            {
                Image = { Color = "0.10 0.10 0.10 0.75" },
                RectTransform = { AnchorMin = "0.75 0.92", AnchorMax = "0.98 0.97" }
            }, "Overlay", IndicatorName);

            container.Add(new CuiLabel
            {
                Text = { Text = Msg("Indicator", player.UserIDString), FontSize = 14, Align = TextAnchor.MiddleCenter, Color = "0.9 0.4 0.4 1" },
                RectTransform = { AnchorMin = "0 0", AnchorMax = "1 1" }
            }, panel);

            CuiHelper.AddUi(player, container);
        }

        private object OnEntityTakeDamage(BaseCombatEntity entity, HitInfo hitInfo)
        {
            if (!config.BlockDamage) return null;
            var player = entity as BasePlayer;
            if (player == null || hitInfo == null) return null;
            return vanished.Contains(player.userID.Get()) ? (object)false : null;
        }

        private void OnPlayerDisconnected(BasePlayer player, string reason)
        {
            if (player == null) return;
            vanished.Remove(player.userID.Get());
            CuiHelper.DestroyUi(player, IndicatorName);
        }

        private void Unload()
        {
            foreach (var player in BasePlayer.activePlayerList)
            {
                if (player != null)
                {
                    player.SetPlayerFlag(BasePlayer.PlayerFlags.Spectating, false);
                    CuiHelper.DestroyUi(player, IndicatorName);
                }
            }
            vanished.Clear();
        }
    }
}